Understanding how closely related species respond to ecological variation and natural selection is central to predicting evolutionary change, especially under rapidly shifting environmental conditions. This study uses perennial sunflowers (genus Helianthus) in the Upper Midwest as a focal system for examining trait differentiation and selection dynamics across time and species. We established multi-year common gardens at two sites in Eau Claire, WI, to experimentally compare functional traits and fitness responses among three widespread Helianthus species: H. giganteus, H. grosseserratus, and H. maximiliani. These species co-occur across the region and often overlap in distribution, where trait divergence may mediate niche partitioning or reflect variation in selective pressures. Comparing selection patterns across species, sites, and years can help evaluate how evolutionary history, resource availability, and climate variation shape trait evolution in wild sunflower populations. This research contributes to broader ecological and evolutionary questions about phenotypic plasticity, adaptation, and species coexistence, providing a long-term dataset for understanding plant responses to a changing environment.
